Continuous forming of complex molded shapes

ABSTRACT

A method, process and apparatus for generating complex shapes without the use of dies, molds, or other fixed tooling. A continuous length or flow of a malleable or fluent material is provided to a forming apparatus which shapes the material, producing a contiguous series of smoothly blended, properly contoured portions of the desired shape. The formation of a shape relies on continuous control of shape-determining variables: the instantaneous cross-section of the shape in a virtual transition surface between the formable and formed material, the rate-of-change of cross-sectional dimensions between sequential cross-sections, the instantaneous angle of movement of the material at any point on the cross-section in the transition surface, and the rate of movement away from the transition surface of the just-stabilized portion of the shape. The material is stabilized as these shape-determining variables achieve the proper values in each portion of the material. The invention further provides a technique for analyzing and modifying a computer model of a desired shape, and for developing a process control datafile from the models.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of PCT application Ser. No.PCT/US92/08505, filed Oct. 6, 1992, which is a continuation-in-part ofU.S. application Ser. No. 07/775/642, filed Oct. 10, 1991, now U.S. Pat.No. 5,266,021, issued Nov. 30, 1993.

BACKGROUND OF THE INVENTION

The present invention relates generally to molding and forming processesand more specifically to the continuous forming of compound-curved(doubly-curved, complex) shapes (such as shell structures) without theuse of molds or dies.

The prior art for mass-producing identical shapes with complex contoursincludes a variety of molding, casting, and die stamping processes.Almost all such processes have relied on single-purpose tooling in theform of molds, dies, or masters. The disadvantages of these processescome from their reliance on such dedicated tooling and the costsassociated with it. In the design and manufacturing stages, a group ofspecialists in product design, manufacturing engineering, and die-makingmust work together, with the time and expense of their collaborationbecoming less predictable as the degree of novelty and complexity of adesired shape increases. Additionally, the required tooling is oftencomplicated and requires continuing highly-skilled maintenance. Finally,tooling that goes in and out of service has continuing overhead costsassociated with storage, including risk of damage, deterioration, andinventory expenses.

These costs, along with the risk of undertaking a project withunpredictable time and expense factors, can reduce the degree ofinnovation or variety a manufacturer is willing to incorporate into aproduct line. At the same time, increasing competitive pressures aredriving the markets for many goods, with the difference between successor failure for a product line or an entire company often depending onthe company's ability to have a quick response to market changes, or tolead the market through product innovation and variety. The capabilitiesfor producing small quantifies of highly differentiated products, oftenon a very compressed timetable, are quickly becoming an absolutenecessity in many fields of manufacture.

There have been various attempts to reduce or eliminate the need forsingle-purpose tooling. For example, U.S. Pat. No. 4,865,796 (Tamura etat.) discloses a technique for forming elongate members for automobiles.The method includes the steps of extruding the material with constantcross-section, continuously removing materials so as to vary thecross-section in the longitudinal direction, and cutting the materialsin predetermined lengths. This has the advantage that there is no needfor molds or for combining separately formed parts, but is limited toshapes that can be formed by the removal of material from a constantprofile of extrusion. There is no provision for longitudinal curvatures.

U.S. Pat. No. 4,770,017 (Yamashita et at.) discloses a technique forforming plates into double-curved shapes. The technique relies onbending and stretch-deformation induced by passing the plate through anentrance roll, flexible rolls, and exit rolls. The flexible rolls canassume various profiles to give transverse curvature while the threesets of rolls are adjusted vertically to control longitudinalcurvatures. Again, this technique has the advantage that there is noneed for approximating dies or manual heating and bending to finalshape, and it develops smoother surfaces than shapes which arerepeatedly punched or hammered. However, multiple passes are requiredfor deeply-drawn complex surfaces, and the flexible rolls requirenumerous wheels with rim shapes which must be varied to form a widerange of plate contours.

U.S. Pat. No. 4,755,334 (Grinun et al.) discloses a molding apparatusthat provides some flexibility and ease of adaptation compared tostandard molds or dies. Specifically, belt-mounted mold segments form amold cavity with opposing mold segments or a continuous facing. Thus, itis possible to mold complex shapes of any length, and the mold segmentscan be rearranged or substituted to mold various shapes. However thesegments have fixed contours, requiring a stock of mold segments foreach shape. Moreover, the precise mating of mold segment edges isdifficult to achieve if the complex contours of the shape extend beyonda single mold segment.

U.S. Pat. No. 4,749,535 (Matsuda) discloses a technique using constantcross-section extruded thermo-plastic material which is introduced intoa contoured molding roll, rapidly cooled, and cut to length. This is asimple apparatus for producing compound-curved shapes with a singleforming surface that does not require pressure or vacuum apparatus forthermoforming. However, the formed shapes cannot have longitudinalconcavities because extruded material would bridge such concavities inthe forming surface, and the rotating roll which bears the formingsurface must be scaled to the size of the desired shape, drasticallylimiting the shape range of a particular molding roll. Thus, the priorart techniques have either yielded to the need for fixed tooling, orhave escaped such need at the cost of being unable to form complexshapes.

SUMMARY OF THE INVENTION

The present invention provides a computer-controlled process andapparatus for generating complex shapes in a single continuous operationwithout the use of dies, molds, or other fixed tooling. The inventionfurther provides a technique for analyzing and modifying a shape, andfor developing process control instructions from computer models or CADrepresentations of desired shapes. The shape-generating process may beapplied to a single homogeneous material in a stretch-deformable,shear-deformable, or fluent state, or to a cornmingled or layered mix ofmaterials types, constructions, or combinations in which separateelements or portions may be differentially moved or shaped.

In brief, the present invention contemplates providing a continuouslength or flow of a malleable or fluent material to a forming apparatus,which shapes the material and then stabilizes it to produce a contiguousseries of smoothly-blended, properly contoured portions of the desiredshape. The formation and stabilization of the shape rely on continuouslycontrolling the instantaneous cross-sectional dimensions of the shape ina virtual transition surface, while simultaneously controlling therates-of-change of the cross-sectional dimensions of the shape, theinstantaneous angle of movement of the material at any point on thecross-section, and the rates of generation (rates of movement away fromthe transition surface) of the stabilized potion of the shape at anypoint on the cross-section.

A unique advantage of the process is a near-instantaneous stabilizationof the formed shape, no matter what the material. The stabilizationensures that no broad-area support is necessary to prevent deformationof the shape. For instance when shaping a thermoplastic material,stabilization is achieved by chilling the surfaces below the material'ssoftening temperature, thereby preserving the imparted dimensions whilethe material is cooled through its entire thickness.

In one class of embodiments, the relative motion is derived by havingthe stabilized material in motion and the forming apparatus stationary;in a second set of embodiments, the molding apparatus moves while thestabilized material remains stationary. In yet a third class ofembodiments, both the stabilized material and the forming apparatus maymove or be stationary at different times in the shape-forming cycle.While a given apparatus for carrying out the present invention is notcapable of generating every possible shape, a particular apparatus iscapable of generating a virtually limitless number of shapes withincertain broad overall constraints.

The invention overcomes limitations of the prior an and has significantnew advantages. Besides eliminating time and cost factors associatedwith fixed tooling, the invention greatly facilitates the design andprototyping stage by allowing single shapes to be produced at a cost nogreater than for mass production. Other advantages are best seen bycomparison with specific prior an in plastics and composite formingprocesses, although the range of applications for the invention goes farbeyond these. Sheet forming embodiments of the invention make obsoleteprior processes for medium and large-scale sheet thermoforming.Apparatus incorporating the invention can accept sheet feed directlyfrom an extruder, avoiding the necessity for reheating or for elaboratehandling apparatus to adapt intermittent forming processes to theextruder's continuous output. The manufacture of paneling, housings,boats, vehicle underbodies and other medium-to-large shell structures bythermoforming processes is therefore a field which the invention candominate.

The invention contemplates embodiments for molding of hollow structuralor functional components. This contrasts with blow molding or rotationalmolding where dies must be made in two or more separable parts, and soare inherently more complex than thermoforming dies, yet areadvantageous because of their abilities to form single-pan hollowbodies. The invention not only eliminates the need for dies; it offersthe further advantages of creating indefinitely long hollow shapes suchas ducting, with varying cross-sections and many nonplanar curves. Suchshapes would require near-impossible size and complexity in multi-pandies, whether for blow or rotational molding. Also, in blow molding thechallenge of laying a parison into a large complex die entails roboticmovement of an extrusion head to achieve uniform control of wallthickness and a low waste factor. The invention has the unique advantageof allowing the creation of continuous, complexly-curved, variablecross-section, hollow shapes in place. A mobile system incorporating theinvention could integrate continuous ducting or paneling right into abuilding, an aircraft, a ship, or other large structures.

The forming of high-strength structural elements and panels is anotherfield in which the invention offers the significant advantages of nofixed tooling and a capability to form long, complex shapes. Since theintroduction of polymeric-matrix fiber composite materials some decadesago, the standard methods for producing shapes have involved thematched-die stamping of pre-impregnated reinforcement materials, thehand or automated layup of reinforcing fabrics and matting followed byresin wetting, the spraying of a mix of fibers and resin, and other suchmethods which all rely on dies or forms. Besides the above advantages,the invention would also offer unique capabilities for creating long,complex shapes from the new class of high-temperaturethermoplastic-matrix composites. Heating of a relatively narrow band ofthe material just prior to shaping would reduce the risks of degradingit, and would aid the efficient use and recycling of the energy employedin heating.

The invention also offers a unique new capability to create structuresin which a variety of materials and components are merged into acontinuous, integrated form. For example a composite sandwichconstruction might be shaped, in which thermo-plastic facings, over areinforced material with a high-strength thermosetting matrix resin,hold the shape while the matrix resin cures. Further, the sandwich mightinclude piping, wiring and ducting, with all these components being fedfrom rolls and coils, and being brought together just prior to theforming process. Discrete components such as sensors and actuators mightalso be merged with the other materials and components prior to forming,and so be merged seamlessly into the resulting integrated structure.

Bending stresses, especially compressive forces within the materialsbeing shaped, are avoided or greatly minimized, and the methods ofapplying smoothly-varied continuous shaping forces allow the forces tobe kept to the minimum values required for working with particularmaterials or materials combinations. Therefore the control elementswhich interact with materials in the shaping operations may often belightly constructed, may exert very moderate forces, and are relativelyinexpensive to manufacture and operate as compared to prior apparatus.

As will be seen, the smoothly varied control of shaping forces isespecially valuable for generating structures from viscous orviscoelastic materials such as polymeric materials above their glasstransition temperatures. A moderate reduction in the forming processrate may reduce the shaping forces required by one or more orders ofmagnitude. The resultant economies in the structural and powerrequirements for the forming apparatus may be easily appreciated.

A further understanding of the nature and the advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-G are schematic perspective and side views of a moving body anda surface tracing array, which aid in showing basic motion relationshipsbetween a continuous cross-section dimensioning mechanism and thematerial being formed;

FIGS. 2A-G are schematic perspective views of forming-related conceptualelements and generated shape examples, both of which aid visualizationof the forming principles underlying the invention;

FIGS. 3A-G are schematic views of three embodiments of a specificforming method employing the invention;

FIGS. 4A-B are diagrams which further elucidate the dynamic relationshipbetween a cross-section dimensioning mechanism and material beingformed;

FIG. 5 is a process overview chart indicating the elements and sequenceof operations of continuous forming systems incorporating the invention;

FIG. 6A is a perspective view of a thermoplastic sheet former with astationary cross-section dimensioning mechanism from which a shape isgenerated by controlling the movement and orientation of the stabilizedportion of the shape away from the mechanism;

FIGS. 6B are assorted detailed views of the cross-section dimensioningmechanism and related elements;

FIGS. 6O-U are assorted views of a drive wheel mechanism which holds,orients, and moves the formed portion of a shape away from thecross-section dimensioning mechanism;

FIG. 7A is a perspective view of a forming apparatus in which thecross-section dimensioning mechanism is moved through space to generatea stationary formed shape from a fluent thermoplastic material;

FIGS. 7B is a perspective view of a variation of the cross-sectiondimensioning mechanism which is integrated with a resin-dispensingmanifold and resin-flow controller;

FIGS. 7C-I are assorted detailed views of the mechanism and resindispenser;

FIGS. 7J-M are assorted views of another variation of the cross-sectiondimensioning mechanism which is capable of assuming nonplanarcurvatures, with a diagram of its operation;

FIGS. 7N-O are side and partial perspective views of a mobile formingapparatus which can generate indefinite-length stationary shapes;

FIGS. 7P-Q are cross-section views of alternative exiting elements ofresin dispensers;

FIG. 7R is a cross-section view of resin dispensers receiving a seriesof components which are interconnected with wiring and integrated into apermeable core material;

FIG. 7S is a perspective view of an apparatus in which the cross-sectiondimensioning mechanism rides on the formed portion of a stationaryshape;

FIGS. 8A-B are perspective and partial front views of a hollow bodyformer which shapes an extruded thermoplastic tube;

FIGS. 9A-C are a perspective view and two schematic side views of athermoplastic sheet former with a simple linear-orthogonal movement ofthe exiting formed shape in relation to the cross-section dimensioningmechanism, and schematic side views of the apparatus at various pointsin a forming sequence;

FIGS. 10A-B are a partial perspective view and a partial side view of aflexible-structure former with yet another variation of thecross-section dimensioning mechanism, while FIG. 10C is a perspectiveview of a cut portion of the formed structure;

FIG. 11 is a block diagram of a system incorporating the sheetthermoforming apparatus of FIG. 6A;

FIG. 12 is a flow diagram of a computer-interactive procedure whichincorporates the conceptual elements of FIG. 2A to develop a suitablecomputer model for use in creating a parallel-operation, multiple-pathprocess control data file;

FIGS. 13A-F are simulations of computer displays an operator mightproduce during the procedure of FIG. 12;

FIG. 14 is a process control diagram for a system incorporating thefluent material forming apparatus of FIG. 7A;

FIG. 15 is a schematic view illustrating the constrained-springprinciple used in certain spline assembly embodiments;

FIGS. 16A-D show a spline assembly using compressed springs;

FIGS. 17A-D show two variants of a spline assembly using pressurizedtubes;

FIGS. 18A-D show a spline assembly using tensioned cables;

FIGS. 19A-G show an embodiment of a cross-section dimensioner in whichpivoting positioning elements are connected through pin bearingsdirectly to the spline assembly; and

FIGS. 20A-G show an embodiment of a stabilizing element in which aflexible containment chamber is carried by an internal spline andencloses flexible footing elements.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Shaping Process Introduction--FIGS. 1A-G

The invention is expressed in a continuous, dynamic shaping process. Thecoordinated movements of final control elements (those interactingdirectly with the formable materials) impart a continuous series ofpredetermined, instantaneous cross-sectional dimensions and slopes tothe material being shaped. Each infinitesimal "slice" of the formedmaterial experiences a cessation of shaping forces in that same instant.The result may be seen as a formed body which is created at a transitionsurface, with the dimensioned and oriented cross-sectional elements ofthe body going from a formable state to a stabilized state as they exitthe surface.

FIG. 1A shows an already formed body 10 which might be created with theinvention. The varying contours of the body make it necessary not onlyto develop a series of cross-sections of the shape, but also to controlthe rate at which they are developed. FIGS. 1B-C show the existent bodyand a hypothetical surface tracer which, though not an aspect of theinvention, will contribute to an understanding of the dynamic variableswhich a forming process utilizing the invention must control.

FIG. 1B shows the body 10 moving linearly and beginning to enter anarray of tracing rods 12, the inner tips of which will slide along thesurface of the body. FIG. 1C shows the body having entered the array.The rods move radially in or out in a vertical plaxtar surface 15 whichis transverse to the direction of movement of the body.

FIG. 1D shows motion vectors at a particular point on the upper midlineof the nose section of body 10. A horizontal vector 20 is identical to amotion vector 22 of the body. Angle 25 (22.5 degrees from the vertical)is the slope of the body, while a vector 30 shows the instantaneousdirection and rate of movement of a vertically oriented surface-tracingrod at this point. The magnitude of vector 30 is proportional to thetangent of the complementary angle (67.5 degrees) of angle 25 orapproximately 2.4 times the magnitude of vector 20. FIG. 1E shows themotion vectors of the tracing rod at several other points along the nosecurve. The magnitudes of the rod-movement vectors 35 go from a 1:1relationship (45 degree slope of surface) with the body-movement vector20 to a zero magnitude, proportionate as in FIG. 1D to the tangent ofthe complementary angle.

FIG. 1F shows the rod vectors along an upward slope 40 of the body, witha constant 1:1 relationship with the body-movement vector, due to theuniform 45 degree slope of the surface. FIG. 1G shows the opposed yetequal rod vectors along a uniform 45 degree downward slope 50.

To appreciate the invention, imagine the tracing rods 12 being replacedby variable-rate linear positioners. The motions of the positioners arecomputer-controlled and emulate the tracing rod motions of FIGS. 1A-G.The positioners act upon a mechanism which recreates the series ofinstantaneous cross-sectional dimensions of body 10. The mechanism actsin turn upon a continuous length or flow of material, impartinginstantaneous predetermined dimensions and slopes to an increment of thematerial's surface, at which instant the shaping process on theincrement ceases. Referring again to FIG. 1D, imagine that vector 20shows the movement of material through the cross-section dimensioningmechanism, while vector 30 shows the movement of the mechanism. Theinstantaneous slope of the surface being formed would depend on theresultant of the motion vectors 20 and 30, as would the instantaneousrate at which the surface is formed. Since the shaping process is smoothand continuous, a replica of this portion of body 10 would be generatedas if being created at a transition surface between a formable materialand a stable shape.

Shape-Generating Principles--FIGS. 2A-G

The process relies on simple principles for the continuous forming ofshapes. FIGS. 2A-G embody these principles in five conceptual elements:a virtual body 60, an axis of generation 65, a transition surface 70, aninstantaneous cross-section 75, and an actual body 80.

In FIG. 2A, the virtual body moves through the transition surface,becoming the actual body. The instantaneous cross-section lies insurface 70 and exemplifies the continuous, smoothly varying series ofcross-sections which exist at the moment of transition. The axis ofgeneration is situated at the center of the bodies and guides them in aparticular orientation towards and away from the transition surface. Inthis instance the movement is linear and the orientation is constantlyperpendicular to the surface.

FIG. 2B shows a curvilinear axis of generation at the center of virtualbody 60 and actual body 80. Body 60 is moving towards the transitionsurface as if rotated about a point 83, while body 80 is moving awayfrom the surface as if rotated about a point 85. Although orientationsof any particular points on the bodies are continuously changing inrelation to the surface, the axis of generation is always perpendicularat the moment of intersection with the surface.

In FIG. 2C a stationary actual body is created by the rotation of thetransition surface about a line 87 (the stationary virtual body and axisof generation are not shown). FIG. 2D also shows the creation of astationary actual body from a stationary virtual body, in this instancewith a linear, nonrotating movement of the transition surface verticallyupward.

FIGS. 2E-G show the creation of three classical surface forms from whichany shape can be composed. FIG. 2E shows a parabolic (or developable)surface 90 which is formed by differential rates of generation betweenthe top and bottom edges as indicated by arrows 92 and 95. FIG. 2F showsan elliptic (or syntactic) surface 97 foraged by progressively greaterrates of generation from the top and bottom towards the center. FIG. 2Gshows a hyperbolic (or anticlastic) surface 100 formed by progressivelygreater rates of generation from the center towards the top and bottomedges. It can be appreciated that sharp surface curvatures, such asthose of a cube's edge and comer regions, are merely extreme examples ofthese surface forms.

The examples of shape generation in FIGS. 2A-G are but simpleexpressions of the forming principles which underlie the invention. Forinstance an axis of generation may comprise a complex series ofnon-intersecting three-dimensional curves. Likewise a virtual body mayincorporate complex contours and curvatures. Finally a transitionsurface may have three-dimensionally variable properties like a rubbersheet, so that the varying instantaneous cross-sections, generated byits movement relative to the axis of generation, may havethree-dimensional curvilinear properties.

Method for Shaping Materials--FIGS. 3A-G

The invention implements these shape-generating principles in a processwhich relies on a specific method for shaping formable materials. Themethod consists of continuously and instantaneously stabilizingincremental portions of a length or flow of a formable material as a setof shape-determining variables are brought to predetermined values sothat the just-stabilized portions become additions to the formed shape.The stabilization consists of changing the state of a material from aformable state to a fixed state which resists further deformation, or ofceasing the application of deforming forces on a material which thenholds the imparted dimensions.

The shape-determining variables are controlled in relation to a virtualtransition surface at which the materials go from a formable conditionto a stabilized state. These variables are: the instantaneouscross-sectional dimensions of the material in a transition surface, therates-of-change of the cross-sections, and the angles of movement anddifferential rates of movement of any portion of the formed material inrelation to the transition surface.

FIGS. 3A-G schematically show the method as employed in threesignificant embodiment of the process. The same reference numerals areused to refer to functionally corresponding elements in the differentembodiments. In FIG. 3A a sheet of heat-softened thermoplastic material110 passes through a cross-section dimensioning mechanism 112 whichresides at, and moves in the plane of, a fixed transition surface 70. Asthe material crosses the transition surface it is instantaneouslystabilized, so becoming an incremental addition to the formed andstabilized body 80. As the material approaches mechanism 112 it isinitially moving at a constant speed across its width as indicated byarrows 115. Body 80 is moved away from the mechanism at a varied ratealong its transverse dimensions, with the maximum rate at the center asshown by arrow 118 and with the minimum rate at the edge, as shown byarrow 120, which matches the initial constant speed of sheet 110. As thematerial is in a continuous sheet, the forces on body 80 are transmittedto the stretch-deformable region 123. The differential rate of movementof body 80 results in the varying stretch-rate in the material at 123,as shown by the arrows 125.

FIG. 3B is a schematic expanded section view of mechanism 112 which isrepresented by a pair of material guides 130 and chiller elements 135.Material 110 is positioned by the guides and is immediately stabilizedas it exits the guides by the flow of a cooling fluid 132 throughelements 135 and against the opposed surfaces of the material, creatingthe formed body increment 80.

In FIG. 3C a liquefied thermoplastic material 140 is delivered through amanifold 145 to mechanism 112, again represented by material guides andchiller elements. The mechanism has rotated through space while smoothlychanging, as shown in FIG. 3D, from profile 147 to the mechanism's finalprofile. The formed body 80 is extruded in place by chilling material140 as it exits the mechanism. The schematic section view of FIG. 3Eshows the dynamics of the forming process. Mechanism 112 issimultaneously translating as shown by vector 150, moving parallel totransition surface 70 (vector 152), and rotating (vector 155). Theresultant of these motions is shown by vector 160. Simultaneouslymaterial 140 is delivered at a velocity 162 which matches that ofresultant 160 so that the stabilized exiting body portion 80 has noabsolute motion. Incidentally, if the mechanism in FIG. 3A had changedthrough the range of profiles shown in FIG. 3D, the exiting (moving)formed shape would resemble the formed-in-place shape of FIG. 3C. Therelative motions between the formed material and the cross-sectiondimensioning mechanism determine the contours of the shape, rather thanthe absolute motions of either.

FIG. 3F shows a flexible stretch-deformable material 165 being shaped tothe dimensions of the body in FIG. 3A. Rather than assuming the actualshape of the desired cross-section 167 of the body being formed, thematerial is differentially stretched across its transverse dimension bymechanism 112, as shown in FIG. 3G, into a variably corrugatedconfiguration. At the same time the material is pulled through themechanism, as in FIG. 3A, at a differential rate 125 which increasestowards the center, resulting in a differential stretch rate, andresultant differential dimensions in the longitudinal ormaterial-movement direction, in exiting body 80. When the flexiblematerial of the body is smoothed out, it resembles the synclastic bodyof FIG. 3A. Similarly, if the mechanism progressively emulates the localdimensions (though not the shape) of the range of profiles shown in FIG.3D, the exiting body would, when smoothed out, resemble the body of FIG.3C.

Thus it can be seen that shaping methods which might appear verydissimilar, and which are applied to diverse forms of materials, areactually a single method implementing the same shape-generatingprinciples. Likewise, the specific embodiments described below may seemdissimilar, yet will be seen to rely on the same method and principles.

Shape Generation As A Function Of Material Motion And Cross-SectionControl--FIGS. 4A-B

FIG. 4A is a table which schematically shows examples of therelationship between the cross-section in the transition surface, theexiting material motion, and the shape being generated. The upper row ofthe table indicates three varieties of exiting material motion, startingfrom the left: a uniform orthogonal motion, a uniformly varyingslow-fast-slow orthogonal motion, and a differential orthogonal motionwith the same velocity gradient as would be achieved by rotating theexiting material about a pivot point below and in the plane of thetransition surface. The second motion case might also be described as atime-referenced or differential temporal motion, while the third motioncase is a space-referenced or differential spatial motion. The leftcolumn shows three behaviors of the cross-section in the transitionsurface. At the top is an unchanging or constant cross-section; next isa cross-section shrinking at a constant rate; and at the bottom is across-section which initially expands at a slowing rate, reversesdirection, and then shrinks at an increasing rate. The second case isone of constant temporal change, while the third case is one ofdifferential temporal change.

The upper left exiting shape, generated at a uniform rate, iscylindrical with a constant cross-section identical to the cross-sectionin the transition surface. The second exiting shape in that row isidentical to the first, though it was generated at a uniformly varyingrate. The third exiting shape is generated as a figure of rotation, inthis case a toms segment, also with a constant or unchanging circularcross-section. The shape is formed as if rotating about a pivot point,with the inner circumference smaller than the outer circumference. Everyinfinitesimal cross-sectional "slice" of the shape is wedge-shaped, withthe thicker portion at the top. This is so because there is a minimumrate of exiting material movement at the bottom of the figure, creatinga minimum length of material per unit of time at that point, withprogressively greater lengths of material exiting in the same unit oftime towards the top of the figure.

The leftmost shape in the next row is conical, with the cross-sectionchanging from a maximum to a minimum size during the forming interval.The constant rate of cross-sectional change, coupled with the constantuniform exiting rate, produces linear slopes on the figure. The secondshape in the row is bell-like, due to the varied forming rates(slow-fast-slow material movement). The slopes are again linear, becausethe exiting material rate is constant between speed changes. However thebeginning and ending slopes are more steeply inclined than in thecentral region of the shape, since the slope of the shape at any pointis a resultant of the rate of material movement and the rate-of-changeof the cross-section. The third shape in the row ("rotary" materialmovement) has a horn shape, being in effect a composite of the toroidalsegment above and the conical shape.

The leftmost shape in the last row has maximum slopes at the ends, sincethe rate-of-change of the cross-section is greatest at these points. Therate-of-change decreases towards the center of the shape as does theslope, with zero rate-of-change and zero slope in the instant that thecross-section stops expanding and starts shrinking. The second shape(slow-fast-slow material movement) has steeper slopes towards both endsthan the first, since the material is exiting at a slower rate at thebeginning and end of the forming interval. Towards the center, theforming rate and rates-of-change of the cross-section are the same as inthe first shape in the row, giving the shapes identical contours inthese regions. The last shape ("rotary" material movement) again hascomposite characteristics, although not so recognizably, of the firstshape in the row and the toroidal segment above.

Since a significant advantage of the invention is its ability to producecomplex shapes with a wide range of contours, both the cross-section inthe transition surface and the exiting material rates must be freelyvaried within constraints of the shape-generating principles and methoddescribed. The slopes or contours of any shape are directly determinedby the resultant of the motion vectors of the cross-section determiningmechanism and the material, with the resultant being definable at avirtual transition surface. The invention accomplishes this byestablishing a predictable geometric relationship between the transitionsurface and the mechanism, and by providing control of the rate anddirection of movement of material at the transition surface.

FIG. 4B schematically shows the variables preferred for processes of theinvention. The first segment of FIG. 4B represents a freely-variedcross-section, with the rate-of-change in any direction likewise freelyvariable. The second segment represents variable control of the exitingmaterial rate at any point on the cross-section. While orthogonalmotions away from the transition surface are shown, implementations ofthe invention need not directly control the material direction. As willbe seen in the embodiments, the angle to the transition surface can bedeveloped as a function of the cross-sectional rates-of-change and thematerial movement rates.

The third segment represents an exiting material motion with a variablevelocity gradient which emulates rotation of the whole body of exitingmaterial about a variable pivot point. This virtual pivot point may notonly change its distance from the center of the cross-section in thetransition surface during the forming interval; it may also rotate aboutthe cross-section in the plane of the transition surface. Implementationof this freely-variable pivot point concept will become clear in theapparatus descriptions to follow.

Other variables may be considered for continuous forming, such asnon-orthogonal relationships between the transition surface and theexiting shape, or non-planar motions and curvatures of the cross-sectiondimensioning mechanism during the forming process. However the variablesof FIG. 4B, in conjunction with a planar cross-section control andtransition surface, allow the generation of a wide variety of shapes. Assuch they serve as the bases for control of the shaping processes inmost of the examples to follow.

Process Overview--FIG. 5

FIG. 5 is a diagram showing an arrangement of elements and sequence ofoperations which exemplify continuous forming processes utilizing theinvention. A three dimensional virtual representation or "CAD model" ofthe shape is taken from a database, analyzed to determine formability ofthe shape, modified as necessary, and used as the basis for generatingsequential numerical instruction sets for the parallel operation ofcontrol elements in a forming system.

Starting with a CAD database 180, the sequence proceeds to acomputerized analysis (represented by two pictorial segments 182 and 183of the diagram) of the shape. Part of the analysis might be performed bya workstation operator and part automatically, depending on complexityof the CAD model, need for modification, and computer programcapabilities. A generally planar complex shape is shown, as well as acomplex though generally tubular shape, as they might be displayed whileundergoing a sequential analysis of intersections with a transitionsurface. The model must satisfy forming constraints on the rate ofcross-sectional change, differential rate of movement through thetransition surface, and shaping forces required for candidate materials.If, for example, some angles on the shape are too extreme, the operatormight change the contours of the model and subject the modified regionsto a second analysis.

Proceeding on, the CAD model is processed to develop sequentialinstructions for process control elements. There are at least threevariables which the shaping process must control. These are 1) asequential series of cross-sections defining the shape; 2) filecontinuous rate-of-change from one cross-section to the next in theseries; and 3) rates of movement of formed material relative to thecross-section in a transition surface. As will be seen in specificembodiments, a fourth critical variable, the slopes, angles, ordirections of movement of material at the instant of transition, can bea function of the dynamic variables 2) and 3). The instructions areaccumulated in a numerical-control (N.C.) datafile 185, which is used bya process controller 190 to control the continuous forming process.

The lower three pictorial segments, designated 191, 192, and 193, of thediagram show examples of computer controlled forming apparatus utilizingthe invention. Segment 191 (to be described below in connection withFIGS. 6A-U) shows an extruded sheet material being shaped by astationary cross-section determining mechanism which is variably curvedby a transverse parallel array of linear positioners. The formed shapeis supported, oriented, and pulled away from the mechanism by drivewheels which engage the shape at the edges and in the center. Segment192 (to be described below in connection with FIGS. 7A-R) shows a fluentmaterial given shape by a variation of the cross-section dimensioningmechanism which is integrated with a resin-dispensing manifold andresin-flow controller. The mechanism is moved through space by acontinuous-motion multi-axis positioner so that the formed andstabilized portion of the shape remains stationary. Segment 193 (to bedescribed below in connection with FIGS. 8A-B) shows a tubular extrusionbeing shaped by a cross-section determining mechanism controlled by acircular array of pivoting linear positioners.

Thermoplastic Sheet Former--FIGS. 6A-U

FIG. 6A shows a thermoplastic sheet former 200. Formable sheet 110 exitsan extruder 205 at a high enough temperature to be stretch-deformed, yetat a low enough temperature to be stretched in the motion directionwithout necking down or breaking loose from the extruder lip. An edgeholder 210, a section of which is shown in FIG. 6B, engages the edges ofthe sheet by indenting it with a wheel train 212. The wheel train coolsthe indentation to near the material's glass transition temperature sothat it is more resistant to deformation, in effect turning anindentation 215 into a stable track in the sheet. Engagement of theindentation in the wheel train prevents sheet 110 from sagging ornarrowing as it advances from the extruder to the sheet former, and alsooffers resistance necessary for transverse stretching of the sheet. Ifthe sheet is thin enough to cool below the forming temperature on itsjourney from the extruder to the former, the sheet would move through aheated tunnel (not shown) bridging the distance between them. If thesheet tended to sag excessively, whether through elastic or inelasticdeformation, a support surface might be provided which levitates thesheet on a thin hot gas cushion (as will be described with reference toFIGS. 6J-K).

Former 200 contains cross-section dimensioning mechanism 112 which isvariably curved in a transverse vertical plane by an array of linearpositioners 217. Each opposed set of positioners may be moved atvariable rates. Sheet 110 passes through the mechanism, beingtransversely shaped and stretched, and is chilled below its glasstransition temperature as it exits. Three sets of exiting-shape drivewheels 220, 222, and 225 engage the formed and stabilized portion of theshape 80, supporting it, orienting it, and transporting it away frommechanism 112. The localized forces exerted by the drive wheels on thestabilized portion are smoothly distributed as tensile forces to theunstabilized portion.

The drive wheel sets (exiting assemblies) may have their rotation ratesvaried to exert differential spatial pulling motions on shape 80, whichresults in differential longitudinal stretching of sheet 110 prior tostabilization. Wheel set 225 is shown rotating at a greater rate thanset 222, which is in turn rotating at a greater rate than set 220. Thesedifferential spatial rates produce the differential horizontalcurvatures shown, as if shape 80 is being pivoted about a distant pointas it is formed.

Differential temporal motions may also be imposed on the stabilizedportion and thereby distributed to the unstabilized portion. Forinstance the drive wheels might have their speeds individually changedto produce varied horizontal curvatures or have their speeds uniformlyvaried in concert to change and forming rate. Their speeds might also beuniformly increased to accelerate the reduction of transverse dimensionswhen the sheet has been transversely stretched by mechanism 112. Tensionalong one axis tends to go towards equilibritun through biaxialdistribution, thereby producing in this instance a reduction in thetransverse dimension through an extension of the longitudinal dimension.This latter differential temporal motion might be especially useful ifthe sheet inelastically deforms and the transverse dimensions need to bereduced in a short spatial or temporal interval.

Finally, the wheels might have their speeds uniformly decreased (whilethe rates-of-change of mechanism 112 are also proportionately decreased)to reduce tensile forces on the just-formed material. Such a control offorces through temporal control would prevent unacceptable deformationof the formed material prior to developing its highest resistance (bybeing chilled below the glass transition point through its entirethickness).

Wheel set 222 is also moved up and down vertically, at a variable rate,by a positioner set 224. The upper wheel is driven through a flexibledrive shaft 223 by a variable-speed motor 227. The variable-ratevertical motion and variable drive rate permits the wheel set 222 tofollow the contours imparted to the shape by mechanism 112. Two or moresets of such movable wheel pairs may be employed as necessary to handlethe weight of shape 80 and to prevent unwanted forces from being exertedon sheet 110 prior to stabilization.

Vertical movement of 222 is also utilized to move the exiting shapevertically relative to the generally horizontal and transverseorientation of the mechanism. An appropriate rate of movement adds avertical component of simulated rotation about a point. Such a motion,when combined with the simulated horizontal rotary motion of the formedshape induced by the wheel sets, produces a resultant exiting rotarymotion of the formed body with a simulated pivot point which can bepositioned and moved freely in space relative to the transition surface.

FIG. 6C shows a portion of mechanism 112 and indicates where the view ofFIG. 6D, an enlarged perspective cutaway view of the mechanism, istaken. Each of the linear positioners 217 terminates in a wheel 230which rides in a groove 232 of an upper flexible spline assembly 235, asdoes an opposed positioner mate with a lower spline assembly 237. Theassemblies comprise layers of flexible strips or splines, through-slots244, retainer pins 247, and pin caps 250. The retainer pins are affixedto inner strips 240 and extend outward to the exterior caps. Theconfined strips 242 are free to slide past one another as shown in thesection view of FIG. 6E, allowing the spline assemblies to assumevariable curvatures as determined by movement of the positioners 217.

The inside faces of the spline assemblies are nested so that thrustforces, as exemplified by arrow 252 in FIG. 6G, are born by bothassemblies. A lateral center hole 254 in each spline assembly, definedby the inner edges of the confined strips, contains a hot gas manifold257, attached to strip 240, which vents through a series of openings 260to the inside faces of the assemblies as shown in FIG. 6J. The gastemperature is maintained at the forming temperature of sheet 110, whichis supported on opposed gas cushions 262 until it moves away from thespline assemblies, thereby avoiding friction, sticking or marring of thesoftened material due to contact with the assemblies.

Appended to the exiting edges of the assemblies are the stabilizingelements 265. Each element consists of a flexible manifold 268 whichdelivers a cooling fluid 270 through a flexible dispenser 272 and ontoopposed surfaces of sheet 110. The fluid instantaneously chills and sorigidities the surfaces to continuously create stabilized portions ofthe shape 80 at transition surface 70 (which is shown in FIG. 6Hsectional view). The exiting shape may be further chilled to removeresidual heat and solidify the material through its entire thickness, asby external water sprays or air jets (not shown). The elements 265 aremounted on double-pin hinges 275 (FIG. 6F) which depend from extensionson the forward retainer pins. The elements are therefore free to followsheet 110 through varying angles while being constrained to move onlyvertically rather than moving or flexing in the horizontal direction.FIG. 6F shows a front view of the elements flexing and displacing tofollow curvatures of the exiting shape. A variety of flexible stiffenersmay be employed to prevent horizontal flexure of the elements betweenhinge attachment points. For instance a strip 277 (see enlarged sectionview-FIG. 6I) may be bonded to the upper surface of dispenser 272, orthe upper face of manifold 268 may incorporate a multiple-pin hingefollowing the bellows configuration.

The constrained-to-vertical movement of elements 265 contributes to apredictable planar-curvilinear locus of stabilization (a virtualtransition surface) of sheet 110, as does the dispensing of chillingfluid starting at the anterior end of dispenser 272, about which thedispenser pivots. The positioning and rates-of-change of the splineassemblies to attain a predictable location and angle of the sheet atthe transition surface can be determined by automatic calculation ofrelative positions of a reference line (say at the geometric center) forthe assemblies and the actual cross-section in the transition plane. Theresult is an actualization of the transition surface concept which issuitable for numerical control of the forming process.

FIGS. 6J-K show enlarged section views of an alternative mechanism 112.The stabilizing elements are as described above; however the splineassemblies contain a central exhaust manifold 280 and two hot gasventing manifolds 282 near either edge. The manifolds 282 deliver gasthrough a pair of vents 284, with one directing gas towards the exhaustmanifold and the other venting towards the spline assembly edge. Apressure differential between manifolds 280 and 282 results in a flowvelocity which reduces the gas cushion pressure to below atmosphericpressure. However the gas cushion is still maintained, since themomentum of the gas carries it in a continuous sheet between the twosurfaces (a variation of the Coanda effect). The upper spline assemblyis held to the positioner 217 by an attached set of flexible strips 290(which form a flexible bearing race), ball bearing 292, and a foot 295with bearing cups. The lower spline assembly is held against material110 and the upper spline assembly by atmospheric pressure acting againstits outer face, as exemplified by the arrows 300. Besides reducing thenumber of positioners which must be employed, the constant forcedistribution along the lower spline assembly reduces the likelihood ofthinning softened sheet 110 by unintended compression forces. Theconstant forces would also prevent the spline assemblies from separatingbetween positioner sets under forces imposed by the entering or exitingmaterial.

Alternative positioners might also be employed to more precisely controlthe curvatures of the spline assemblies. For instance the opposedpositioners might be staggered so that those on one side are placedbetween rather than in line with those on the other side. Also, eachpositioner might be variably moved transversely to align with points ofextreme curvatures or maximum deflections. As a final examplespline-engaging wheels 230 might be variably driven so that the splineassembly can be flexed by tension or compression forces between any twoadjacent wheels.

FIGS. 6L-M show a spline assembly end guide 310 comprising a fixed guidebed 312 and opposed fixed guide wheels 315. Left and right end guidesserve to hold the spline assemblies fixed in relation to transitionplane 70 prior to engagement with the positioners 217. Left and rightpairs of guide wheels might have opposed reel spring mechanisms to holdthe spline assemblies centered as they move in and out in response tochanging cross-sectional dimensions. Alternatively the spline assembliescould be attached by a pivoting foot to central sets of positioners.

A bracket 317 is mounted below the end guide and holds thevariable-speed drive motor 320, which is connected by a flexible shaft322 to one of the drive wheels 220. FIG. 6M shows an end view of thecomponents with the motor and bracket 317 removed. The edge of formablesheet 110 passes from edge holder 210 through a slot 314 in bed 312, andbetween the opposed stabilizing elements 265, turning at the transitionsurface 70 into the edge of shape 80, which then passes between drivewheels 220. The cutaway 313 in bed 312 allows the stabilizing elementsto contact the exiting sheet 80. The wheels 220 are mounted in curvedslots 327 and pressed against sheet 80 by a pair of springs 330. Thecurved slot and spring arrangement allows wheels 220 to passively trackthe stabilized sheet edge as the vertically movable wheel set 222controls the orientation and rotation rate of exiting shape 80. Amultiple-component construction of the wheels allows them to track thesheet edge through horizontal curvatures, as will be shown in followingfigures.

FIG. 6N shows alternative movable end assemblies which add other degreesof control to the sheet forming process. Together withhorizontally-pivoting edge holders 210, these allow the edges of sheet110 and shape 80 to move in and out. The increased slot depth in theguide bed allows the width of a horizontal flange to be varied.Additionally such horizontal positioning control, coupled with moving ofouter sets of the positioners 217 out of contact with mechanism 112,would reduce the necessary amount of transverse stretching of sheet 110when forming narrow shapes of deep cross-section. Each opposed end guideassembly might also be moved vertically up and down. This, when combinedwith the horizontal positioning, would allow each of the opposed edgesor flanges of a shape to be formed differently and with a great degreeof three-dimensional curvilinear freedom.

FIG. 6O shows side views of the movable drive wheel set 222. The lowerwheel 332 is not driven and has a flexible spring section 334 in itssupporting shaft. This permits the wheel to passively orient to shape 80and so remain opposedly positioned to drive wheel 338. FIG. 6P shows analternative assembly for more precisely controlling the movement andorientations of a drive wheel set. In this case movement of the wheelset is controlled by the actions of a rotary positioner 340 and a camset 342 on a wheel shaft 344.

The cam set maintains a fixed-distance relationship between a wheeltangent point 346 and transition surface 70. Maintaining thisrelationship obviates the need to compensate for wheel diameter whengenerating N.C. instructions for the rotary speed and vertical movementof the drive wheel set. Additionally, the precise alignment of wheeltangent points reduces the likelihood of undesired torquing forces onthe exiting shape, as would occur if the opposed drive wheels were farfrom alignment. For the highest degree of precision in driving andoftenting the exiting shape, edge drive wheel sets as well as two ormore central sets of this type would be employed. Alternative exitingassemblies might also be employed, to augment or substitute for drivewheel assemblies. For instance robotic arms with friction-engaging endeffectors might support, orient, and transport the stabilized portion ofthe shape.

FIGS. 6Q-U show details and operation of a drive wheel. FIG. 6Q showsthe wheel's major components, a central axle 350 and spokes 352, eachholding a bi-axially orienting foot 354. FIG. 6S schematically shows awheel driving exiting shape portion 80 which has a horizontal rotarymotion component 358. During the interval in which a wheel foot is incontact with the surface the differential rate of motion across itswidth causes the foot to pivot out of line with the wheel axle as shown.A swivel 356 (FIG. 6R) may also be necessary to allow the plane ofrotation of the wheel to align with the angle of movement of the exitingshape portion 80.

FIG. 6T shows an opposed pair of feet pivoting transversely to adapt tothe transverse orientation of the shape portion. FIGS. 6T-U also showthe two-element pivot arrangement which maintains a constant-distance,fixed drive-point 360 between the wheel feet through a wide range ofexiting shape orientations. Bearing race 362 has a circular curvaturecentered on the drive-point. Pivot 365 allows the foot to pivot out ofline with the wheel axle. The fixed relationship of drive point 360 tothe wheel axle's center assures that the driving radius of the wheel isconstant; therefore the ratio between the wheel's rate of rotation andthe rate of movement of the driven surface is always constant. FinallyFIG. 6T shows a compliant region 368 on each foot which aids the feet inmaintaining substantial contact with the exiting shape despite itscurvature.

In summary, the stationary transition surface concept of FIGS. 2A-B isactualized through the interactions of spline assemblies, stabilizingelements, and drive wheels contained within the forming apparatus 200.Also, the shaping method of FIG. 3A has been given an explicitembodiment. The spline assemblies shape the material into a sequentialseries of smoothly varied cross-sections and control the rate-of-changebetween cross-sections. The stabilizing elements move as if residing ina stationary planar transition surface, chilling and rigidizing thematerial as it is shaped. Finally, the drive wheels control the rate ofmovement and orientation of the stabilized portion of the shape awayfrom the transition surface, and so control the rates, differentialrates, and angle of movement of material at the transition surface.Further embodiments of the invention will actualize the movingtransition surface concept of FIGS. 2C-D, show the fluent materialshaping method of FIG. 3C, and show the flexible material shaping methodof FIG. 3F.

Extrude-in-Place Former--FIGS. 7A-S

In FIG. 7A a stationary shape 80 is generated by movement through spaceof a variation of mechanism 112 which is integrated with aresin-dispensing manifold and resin-flow controller. The mechanismreceives a thermoplastic liquid from a liquifying extruder 405 and ismoved and oriented by a continuous-motion multi-axis positioner 400,describing a rotary motion as shown previously in FIG. 3C, while at thesame time undergoing a curvilinear translation as shown in FIG. 3D. Thedispensing rate through the mechanism is differentially varied along itscurvature so that, at any point, the exiting rate of the resin is equaland opposite to the resultant motion of mechanism 112 at the moment ofstabilization through chilling. As a result the material being added toshape 80 is at zero motion relative to the stationary shape, and so hascontours which smoothly blend with the shape. The mechanism might alsobe incorporated in a stationary forming apparatus as shown in FIG. 6A.In such an embodiment the exit assemblies would transport the shape awayfrom the dispenser, matching the rate and angle of movement of thestabilized portion to the rate and angle of movement of the materialbeing formed at the moment of stabilization.

FIG. 7B is a perspective view of the integrated mechanism, while FIGS.7C-D show enlarged perspective cutaway views of significant componentsand portions of the mechanism. A manifold element 415 has a corrugatedaft region 417 to aid flexure, and a multiply-tubular frontal region 420which necks down to an exiting slot 422, to which is attached astabilizer (chilled fluid dispenser) 272.

A curvature-controlling assembly 425 is mounted on a pair of booms 427and comprises the following elements. A ball bearing retaining strip 430(FIG. 7C) is bonded to opposed outer faces of each tube element ofregion 420. Opposed spline assemblies 432 are composed of strips andretainers as previously described, though they differ from these earlierassemblies in having bearing grooves or races 434 on their inner facesand in having the contoured outer edges of the strips define a pair ofbeating races 436.

A roller chain 438 interconnects to each opposed spline assembly througha series of brackets and bearings 440 rotating on chain pins 442. Theupper arms of each bracket have a pair of hydraulic or pneumaticpositioners 445 connected with sleeve bearings to a series of pins 447,which are mounted on the brackets 440. Each positioner is connected to apressurized fluid controller 450, mounted on the posterior end of eachchain pin, which delivers to or exhausts fluid from either side of apositioner's piston.

FIG. 7D shows exiting slot 422 with a series of built-in resinflow-control assemblies 455, each consisting of a pair of opposedexterior brackets 457 and a connecting spine 460 around which is mounteda liquid resin flow-controller 462. Each bracket has nested bearings 464tiding in races on a pair of opposed spline strips 466 which are bondedto the outer faces of slot 422. Each flow-controller consists of aflexible shim-spring sleeve surrounding a bladder which communicatesthrough a tube 468 with a pressurized fluid controller 470 mounted tothe anterior end of chain-pin 442. A chiller element comprising achilled-fluid manifold robe 472, communicating tubes 474, and dispenser272 is affixed to each lip of the exiting slot.

FIG. 7E shows components of the mechanism in cross-section and aim thelocation of transition surface 70, at the point on dispensers 272 wherechilled fluid first exits. FIG. 7F schematically shows a topsection-view of resin flow-control assemblies 455 and a front view ofthe controllers blocking resin flow to various degrees. FIG. 7G shows across-section of the chilled-fluid dispenser flexed into positionsdetermined by the direction of movement of mechanism 112. The horizontallocation of surface 70 relative to the mechanism is dependent on theangle of movement of the mechanism in relation to the just-stabilized(and stationary) portion of the formed shape.

Some fluent materials may be formed by a resin-dispensing mechanismwhich does not have flow controllers in the exiting slot. If thematerials are of low viscosity and so can flow under relatively lowpressure, the back pressure caused by solidification of the materialwhen stabilized may serve as a locally variable flow control. Thechilled fluid dispensers must be able to hold the fluent material to acontrolled thickness, i.e. not be susceptible to bulging out or pinchingin on the material as it is stabilized.

FIG. 7H shows a variation of mechanism 112 and a dispensing mechanism inwhich the curvature controlling assembly engages the dispensing manifoldfrom one side only. A bearing retaining element 480, bonded to each tubeelement as are elements 430 in FIG. 7C, has bearing cups on the anteriorand posterior ends. A pair of continuous spline assemblies 482 havebearing races defined along anterior and posterior faces, along whichbearings held in the cups of element 480 and brackets 440 are free tomove as curvatures are imposed on the manifold. The exiting resin 140 ischilled on one side only.

FIG. 7I schematically shows curvature controlling assembly 425 imposingextreme curvatures on (dotted lines representing) manifold 415. Thereare many factors which determine the minimum radii which can be formedacross transverse dimensions of a shape. These include flexibility ofspline assemblies, positioner size and extensibility, flow controllerspacing and dimensions, conforming capabilities of the stabilizingelements and the like.

FIG. 7S shows a bail-chain segment 490 which replaces roller chain 438in an alternative curvature controlling assembly with nonplanarcurvilinear capabilities. FIG. 7K diagrammatically shows a variation ofmechanism 112, with nonplanar curve-assuming capabilities, movingvertically downward to form a shape. The mechanism is free not only toflex in the plane of motion as shown at top; it may also curve laterallyto form the bulge or undercut shown in the middle of the figure. Thevirtual transition surface associated with the mechanism is alsononplanar.

FIG. 7L shows a cross-sectional view of the mechanism, while FIG. 7Mshows a partial rear view. The positioners 445 are mounted in angledpairs on twin brackets attached to each bail section of chain 490. Thepositioners connect to the brackets with ball pivots rather than pin andsleeve pivots, and so can assume non-planar relationships with oneanother as each positioner independently extends or contracts. The resinmanifold 415 is circular in cross-section so that it may flex in anydirection, and the dispensers 272 have a very flexible structure whichhas progressive transverse extensibility towards the ends. Suchproperties in the dispensers are necessary to allow them to flex toextreme angles, and can be achieved by a waffled or corrugatedconstruction.

FIGS. 7N-O show a mobile forming system capable of generating anindefinite-length shape 80. A pair of opposedly mounted mechanisms 112are variably moved and oriented by a multi-axis positioner on adirectionally controlled cart 410. The twin mechanisms may have thecapability to form two separate shapes or a single hollow shape in twosections.

FIG. 7P shows two opposed manifolds with a slight variation from that ofFIG. 7H. The inner lips are shortened, and the chilled fluid dispensersare shaped so as to urge opposed streams of resin into contact beforebeing chilled. The opposed manifolds are shown (dotted partial figureson right) initially moving vertically towards one another, creatingvertical portions which are merged into a single portion of a shape asthe dispensed resin streams contact one another and the manifolds movein concert horizontally.

FIG. 7Q shows an opposed pair of manifolds with another slightvariation, in that the resin streams are dispensed towards each other.The resins flow into a permeable core material 495 to create a compositeexiting sheet structure 80. The core material can be configured into adeformable sheet which is variably stretched by tension developedbetween the stabilized portion of the shape and tensioning rolls whichprecede the dimensioning mechanism. A differential relative motion isproduced between the entering sheet and the exiting sheet, which isembedded in stabilized resin, resulting in a forming method similar tothat of FIG. 6 though with the dimensioning mechanism (and associatedtransition surface) in motion.

The core might contain multiple components or materials. FIG. 7R shows aseries of components 497, interconnected with wiring and integrated witha permeable core material. The local flexibility of the resin manifoldallows the components to move through the mechanism, while localizedcurvature control permits flexure across the transverse dimension of themechanism to conform to the components. The resin flow may be turned offacross the body of the components yet embed their edges, while resindelivered from the underside permeates the core material and anchors thecomponent firmly in the core material as the resin solidifies.

These integrated dispensing and dimensioning mechanisms might also havemore than one curvature control assembly. For instance if highly viscousresins are to be dispensed, high pressures in the flexible manifoldmight necessitate a powerful curvature controller which acts on theanterior portion of the manifold. This controller might have fewpositioners and merely approximate the curvatures, with an additionalfine curvature control assembly such as 425 mounted on the forwardportion of the manifold.

FIG. 7S shows a forming apparatus with a variation of mechanism 112which does not rely on the multi-axis positioners 400 shown in FIGS. 7Aand 7N. Instead the mechanism is carried by a set of drive wheels whichride on the formed portion of a stationary shape. Depending on thecomplexity of shapes to be formed, these drive wheel sets might simplypivot on supports extending from the mechanism and rotate against theformed shape under spring pressure. For a higher degree of control, amulti-axis adjustment capability might include moving the wheel supportson two axes while angling and rotating the drive wheels to followcomplex contours.

Summarizing, the moving transition surface concept of FIGS. 2C-D isactualized, and the fluent-material shaping method of FIG. 3C isembodied. A mechanism 112 receiving fluent material is moved throughspace by a multi-axis positioner, or alternatively is carried andoriented by a set of drive wheels which ride on the formed shape. Theexiting material has its velocity variably controlled across thedispensing slot of a manifold by local flow controllers, at a rate thatopposedly matches the rate of movement of the dispenser so that theformed potion of the shape is stationary. Alternately the exitingmaterial has its velocity controlled by the back pressure of thejust-stabilized portion of the shape. A chilling element or elementsstabilize the material as it exits the dispenser, in effect creating atransition surface. The exiting angle of the fluent material in relationto the transition surface is guided, at the moment of transition, byflexure of the chilled-fluid dispenser as it follows the curvatures ofjust-stabilized portions of the shape.

Further Examples of Apparatus--FIGS. 8-10

FIGS. 8A-B show a thermoplastic hollow-body former 500 which producesseamless shapes. The extruded tubular feedstock is engaged by avariation of cross-section determining mechanism 112 from the outsideonly. The spline assembly of the mechanism consists of the top splineassembly of the mechanism shown in FIGS. 6K-L, with the material heldagainst the mechanism by atmospheric pressure. The angles which can beimparted to the exiting material are limited by the tendency of thematerial to pull away from the mechanism more readily than from adouble-element mechanism. The minimum circumference of a formed bodywould depend on the capability of the tubular extrudate to be neckeddown by tensile forces, unless the extruding apparatus has a significantvariable-diameter capability.

FIG. 8B shows a passive inner assembly 505 which presses against andsupports the material from the inside, but only at the opposed regionswhere the outer spline assemblies come together as they bend around theend guide wheels. The material separates from the outer assemblies asthey curve around the wheels (being pulled away by elastic forces withinthe material) and is supported from within on a hot gas cushion aspreviously described. Spline-type inner mechanisms, held against theinside of the material and the outer spline assemblies by a pressuredifferential as in the FIGS. 6J-K, might also be used in conjunctionwith the assembly 505, being carded on slides so that they event alongthe assembly. Alternatively, control elements could be mounted on thefront inner face of the extruder die to control an inner cross-sectiondetermining mechanism. There might also be an inner dispensing mechanismto inject filler materials like foams inside the shape as the exitingmaterial is stabilized.

To create long shapes with extensive curvatures, the dimensioningassembly and extruder might be variously moved and oriented while theformed portion of the shape is being simultaneously transported. Thiscapability would reduce the need to swing the formed potion through anever-greater volume of space as it lengthened. The same capabilitiescould be embodied in a forming apparatus incorporating a fluent materialdispensing and dimensioning assembly.

FIG. 9A shows a sheet former 515 in which the exiting shape has asimplified motion, being moved linearly at a constant rate. Complexcurvatures may be developed by variable rates-of-change of thecross-section determining mechanism; however the shapes will lack"whole-body" currants which emulate rotation of the exiting materialabout a point, and will have planar flange or edge regions. FIGS. 9B-Cschematically shows mechanism 112 moving "downstream" (FIG. 9B) at thesame rate as the feedstock to facilitate forming steeply inclinedportions of the exiting shape, and then moving back "upstream" (FIG. 9C)during periods of little dimensional change.

A moving shuttle 525 (FIG. 9B) may facilitate forming by further heatingthe sheet or pre-forming it with the "corrugating" deforming methodshown in FIGS. 3F-G (and further described below with reference to FIGS.10A-B). Such a method might be employed in the longitudinal (materialmovement) direction as well as in the transverse direction, to givefurther dimensional control of the perform. These capabilities would beof advantage especially for the forming of extreme contours in materialswhich require substantial deforming forces, such as fibrousthermoplastic composites. The shuttle might also be used to minimize theamount of material which is deformed as mechanism 112 transverselystretches the sheet. FIG. 9B shows the shuttle closer to the mechanismat a point of extreme dimensional change in the formed portion of theshape in a small time interval. FIG. 9C shows the shuttle further fromthe mechanism at a point where there is little dimensional change. Theshuttle might be moved even further from the mechanism as the sheet istransversely stretched to increasingly greater dimensions without theneed to return quickly to reduced dimensions.

FIGS. 10A-B show a flexible-structure former which bonds two deformablefacings 540 to a series of vertically-oriented, transversely-disposedflexible ribbing strips 545. The cross-section dimensioning mechanismradically differs from the curvature-assuming mechanisms previouslyshown, instead consisting of an array of deforming elements 550. Theindividual elements move deforming rollers 552 vertically tolocally-variably stretch the facing materials across the ribbing stripguides 547. The wheels of rotary drive elements 560 variably stretch thefacing materials and ribbing strips in the longitudinal ormaterial-movement direction, and then bond facings to ribs, stabilizingthe construction. The bonding point for each fib lies in a virtualtransition surface as previously described; however in this case thetransition surface is nearly reduced to a fixed line, since the planararray of drive wheels are fixed in location. A portion of the resulting"I-beam" sandwich construction is shown in FIG. 10C. The shape may bepressurized, filled with liquids, or filled with a curing foam materialto form a permanent structure. The spaces in the construction might alsocontain components which are fed in between the ribs as the shape isformed.

In this embodiment the forming process is limited to flexible materials.The exiting shape 80 is held in a planar corrugated configuration at themoment of transition, while its final shape may have complexthree-dimensional curvatures. An advantage of the process is that thematerials do not have to be guided into the actual series ofinstantaneous cross-sections as required with rigid materials; thereforea flexible spline-type dimensioning mechanism is not required. Also,extremely high deforming forces can be imposed on the materials due tothe multiplicity of drive and deforming elements in a simple planararray.

A narrow former of this type would be capable of generating very widestructures by adding formed material in successive passes to alreadyformed materials. The former could be moved relative to the formedportion of the shape in a simplified linear constant-speed motion whilecontrolling complex shaping variables. Additionally, such a simpleformer could be used to create performs for use in a conventionalprocess such as (cavity-mold based) resin transfer molding, or toperform a material for the resin-permeating process shown in FIG. 7Q. Afibrous matting might be shaped, generally holding the dimensionsimparted to it at the instant that deforming forces cease. Alternativelythe matting could have a thermoplastic binder which is heated forforming and then chilled to assure more precise and stable dimensions ofthe perform until its use.

System Block Diagram--FIG. 11

FIG. 11 is a detailed block diagram corresponding to the high-level viewof FIG. 5 for a system incorporating the sheet-forming apparatus 200 ofFIG. 6A. Corresponding reference numerals are used. The first (uppermostblock) shows the elements required to develop process controlinstructions. CAD database 180 of an approximate shape is modified by aworkstation operator to meet the forming constraints imposed by theapparatus and the formable material. Control element paths aredetermined or approved by the operator, and the path data are compiledinto numerical-control (N.C.) datafile 185 which process controller 190uses to operate various elements of the apparatus.

The second block shows a main process control CPU which takesinstructions from the N.C. datafile and feeds parallel timing andcontrol instructions to three subsidiary process controllers. These inturn operate groups of control elements (see third block) in parallel toexecute three sets of forming operations.

The cross-section controller operates linear positioners 217 whichcontrol both the curvatures of the final control element (splineassembly 112, which interacts directly with the sheet material) and therates-of-change of the element through a sequence of cross-sections. Thematerial-exiting-rate controller determines the varying rotation ratesof drive wheels 220, 222, and 225 which pull on the exiting stabilizedshape. The exiting-shape-orientation controller operates linearpositioners 224 which position vertically movable center drive wheels222 and variably control their rates-of-change through the movementsequence.

The fourth block contains representative feedback control sensors whichtrack the relevant forming variables in the three groups of operations.The left group of sensors feed back to the cross-section controller(through the main CPU as shown, or directly to the controller). Thesensors may indicate positioner extensions, spline assembly curvatures,cross-sectional dimensions of the exiting shape at the transitionsurface, rates-of-change or any other factors which can give quickfeedback on variances from the desired instantaneous cross-sections ofthe stabilized shape.

The center group of sensors feed back to the material exiting ratecontroller and may consist simply of rotary encoders for each drivewheel motor, although direct rate sensing of the exiting shape at thetransition surface may also be desired. The right group of sensors feedback to the exiting shape orientation controller, and read the verticalpositions and position rates-of-change of the drive wheels or of potionsof the exiting shape at the transition surface. The vertical positionrates-of-change can be compared to the drive wheel motor rates to give"whole-body" radial curvature data.

Many or all of these sensing functions might be performed by a singlesensing system which reads position, contours or angles, and movementrates of the exiting shape at the moment of transition and at one ormore distant points. Commercially available laser-based sensing systemsare capable of measuring profiles, surface rates of movement, anddistances from a reference point or line.

Numerical-Control Datafile Development--FIGS. 12-13

The generalized flowchart of FIG. 12 exemplifies a computer-interactiveprocedure to prepare an N.C. datafile for control of a processincorporating the invention. The procedure involves analyzing andmodifying a computer model of a desired shape to fit within processconstraints, evaluating a formable material, compiling the controldatafile, and viewing a simulation of the forming sequence prior torunning an actual shape generating process.

There are many factors to consider regarding a particular complex shape,the materials from which it can be formed, and the capabilities of aforming apparatus. Hence such a process-specific evaluation procedure isa necessary adjunct to a continuous forming system if a considerablerange of shapes are to be generated. To this end, the procedure includesa number of decision nodes 600, 610, 620, 630, and 640 at which it isdetermined whether to proceed with the current parameters or revisethem.

The conceptual elements shown earlier in FIG. 2A can serve as afoundation for the procedure. Utilizing these elements, FIGS. 13A-F showrepresentative computer displays of a shape and onscreen "tools" thedesigner might utilize to make the interactive procedure relativelysimple and intuitive. Beginning the procedure, the virtual body isdisplayed on the screen in FIG. 13A. The designer may notice sharp radiior extreme angles which are not essential to the function of the shape,and may modify them so as to reduce the rates of movement or rotation ofcontrol elements which will form the final shape. FIG. 13B has twoviews: the original body in profile at the top, and the lower body whichshows the designer's reduction of the central bulge's height and itsbeginning and ending slopes. Such a change, besides reducing thelikelihood of exceeding the operating limits of control elements, willpermit the actual body to be formed at a faster rate.

FIG. 13C shows the virtual body oriented on three axes to a startingposition in relation to a zero point on the transition surface, hererepresented by vertical and horizontal axes of a set of X-Y-Z coordinateaxes. These coordinates will be "mapped" onto numerical controlcoordinates when compiling the N.C. datafile. A polar coordinate systemmight alternatively be employed, with virtual body orientationestablished with the origination point on the transition surface.

FIG. 13D shows the establishment of a portion of the axis of generation(solid line) and a sequence of cross-sections perpendicular to the axis.Also shown is a tentative modification of the axis (dotted line),intended to reduce the rate-of-change of control elements. Regions ofthe interior surface may also be viewed and modified, especially if adouble-shell structure is to be formed with differing contours on theinner and outer shells.

FIG. 13E shows evaluative views of portions of the body at selectedextreme regions, as well as visual "tools" which might be employed bythe designer. The upper left portion is being compared against an angletool set to the maximum angle which the cross-section dimensioning finalcontrol element can form at a minimum bulk material feed rate. The lowerleft portion is compared against a radius tool showing the minimumradius permitted by the final control element. The right portion iscompared against minimum and maximum curvature tools which showcurvatures permitted by differential rates of material movement, inrelation to the axis of generation, at the minimum feed rate.

FIG. 12 can now be described in view of the above description of FIGS.13A-E. Decision node 600 follows this evaluation of slopes andcurvatures, and causes the procedure to loop back to the simplestmodification, a repositioning of the axis of generation, if the testsshown in FIG. 13E fail. A more complex decision node might also causethe procedure to loop back to modification of the body if calculationshowed that no movement of the axis of generation could satisfy formingrequirements.

After an acceptable "best fit" development of the virtual body, theprocedure continues from node 600 to a quantitative analysis ofcandidate material properties in relation to forming apparatuscapabilities. Specifications are usually furnished by material producersand include processing temperatures, viscosities, elongation factors,tensile strengths, etc. Equations are often available to determinedynamic factors, such as flow rate with varied pressures andtemperatures, and resistance to shear or stretching at varied rates.Control elements of a forming apparatus also have operating limits whichmay include maximum and minimum flow pressure or material movementrates, rates-of-change, pulling-force limits, spline assemblydeformation limits and the like. A material with which the designer isunfamiliar may be initially evaluated at the minimum bulk feed rate tothe forming apparatus.

Decision node 610 is a three-way node that follows the comparison ofmaterial properties to apparatus capabilities. If forces on theapparatus are too great or if differential movement rates through theapparatus are too slow or too fast, node 610 invokes node 620, at whichthe designer may choose another material or modify the shape to bringthese factors within operating parameters. Node 610 leads to an increaseof bulk material feed rate if forming rates are slower than the slowestrates of the varied forming apparatus control elements, and invokesdecision node 630. Node 630 allows for incremental increases of the bulkfed rate until it is within suitable limits. If the forming forces andrates are already within limits, node 610 leads to the preparation ofcontrol element paths.

FIG. 13F shows the virtual body reduced to a small number of definingcross-sections, with emphasis given to control element paths. Acomprehensive set of control element paths have been generated along thecomputer model, and are related to the axis of generation by theirintersections with the perimeters of the reference cross-sectionspreviously established along the axis. The axis of generation is alsoshown (bold solid line) as is a general representation of the formingapparatus at the transition surface. Interactive modification of thepaths or axis of generation at this stage can give another degree ofcontrol over the final shape, such as producing a localized deformationor affecting the degree of material stretch and so the thickness of ashell structure in a particular region. Such modification toward the endof model development would also permit iterative production of variedshapes without going through earlier stages of the design andmodification process. For instance another decision node might beintroduced to permit the generation of variations which are immediatelysubjected to process simulations, with those which fall outside ofproduction limits being rejected and the acceptable ones being queued upfor actual forming trials.

The designer may then select a specific portion of the virtual body fora trial production run. For instance regions of extreme dimensionalchange or stretch-elongation might be selected as a test section withoutthe need to generate a whole shape. Following this selection, a trialN.C. datafile is compiled. Since all control elements of the apparatusrun simultaneously, at this stage a time factor is introduced tocoordinate the parallel operation of the elements. To form the datafile,the starting point on the axis of generation is aligned with the zeropoint in an X-Y-Z or polar coordinate system for the physical apparatus,and a timed sequential series of cross-sections are "mapped" into thecoordinate system so that there is a one-to-one correspondence betweenthe virtual body data and the numerical-control data.

The application program for the procedure then processes the N.C.datafile to run a visual simulation of the shape-forming sequence. Arate of movement of the computer model relative to the transitionsurface is established. The model passes through the surface with theaxis of generation being held perpendicular to and coincident with thezero or origination point in the transition surface, while the virtualand (simulated) actual bodies are variably moved and angled along withthe changing orientations of the axis of generation as a whole. Thismight be an animated sequence which makes explicit the shape-determiningvariables and highlights the regions which approach the forming limitsof the apparatus. The variables include the sequence of cross-sections,the rate-of-change of cross-sections, rates and differential rates ofmaterial movement through the transition surface, and relative anglesand orientations of the exiting shape to the transition surface.

The designer is then given a final decision node 640 prior to running anactual forming trial. A more complex node might have multiple decisionpaths to include modifications or additions to the virtual body,different starting orientations, adding portions of the shape to runthrough simulated forming and so forth.

In summary, the conceptual elements of FIGS. 2A-G serve as the basis fora computer-interactive procedure or application program which a designeruses to develop acceptable material and control element paths and rates.The overall objective of the procedure is to facilitate the designprocess and to aid in the full use of apparatus incorporating theinvention. The procedure includes modifying a computer model of theshape as necessary, evaluating materials for suitability, evaluatingcapabilities of the apparatus to form the desired,shape from candidatematerials, establishing geometric paths for the varied control elementsof the forming apparatus, introducing parallel timing of the operationof the control elements to coordinate the positions, rates andrates-of-change of the control elements, compiling a numerical-controldatafile to operate the control elements in parallel, and testing thedatafile in a process simulation. Such a procedure or program isnecessary for realizing the full advantages of the invention, and so maybe considered a key element of a forming system incorporating theinvention.

Process Control Diagram--FIG. 14

FIG. 14 is a process control diagram for a system incorporating thefluent material forming apparatus of FIG. 7A. The beginning conditionsinclude a starting material feed pressure to meet maximum flow raterequirements, control elements in position to form the startingcross-section, the cross-section dimensioning mechanism in the properstarting location and orientation, the material flow controllers off,and the timer for parallel operation of control elements turned on andprogressing to the forming sequence start. Other checks might precedethe forming, as of resin temperatures, chilling fluid temperatures andpressures, and full-range operation of various control elements.

The forming sequence then begins and proceeds with the continuouslyparallel control of three groups of shaping variables. These include thesequential series and rates-of-change of cross-sections, flow rates anddifferential flow rates of the fluent material, and the continuousmovements and orientations of the cross-section dimensioning mechanism.

Feedback control is implemented to keep the three groups of shapingvariables within desired ranges. The sequence continues until thedesired shape is completely formed, or the process is interrupted due toan apparatus malfunction or the development of excessive error ingeneration of the shape.

Flexure-Resisting Spline Assemblies (FIGS. 15-18)

FIGS. 15, 16A-D, 17A-D, and 18A-D show spline assemblies incorporating aconstrained spring element or elements. While the primary purpose of theelements is to control the linearity and flexure of spline assemblieswhich stretch-deform or shear-deform materials, the elements can servein any cross-section dimensioner to resist weight or other deflectingforces.

Such elements can furnish resistance to flexure until a predeterminedforce threshold is reached, after which the loaded portion begins todeform. Further, the characteristics of the imposed curvatures can beinfluenced or controlled by combining the constrained-spring elementswith additional components which cause nonlinear variations in the forceloading on the spring elements, or by designing the spring elements tohave nonlinear responses to varied loading. Such control permits, forinstance, the forming of circular arcs between three control pointsrather than parabolic arcs.

FIG. 15 shows conceptually the constrained-spring principle which isemployed in the various embodiments described below. A spring 700 has anunloaded length of a. The spring is compressed and held in place by atensile constraint 702, following which the compressing force isremoved. To further compress the spring, a force greater than theoriginal compressing force must be applied. The same principle can alsobe applied in the reverse manner to a spring under tension. A springelement can be elongated by tensile forces, held in that condition by acompression-resisting element, have the tensile force removed, andremain at the elongated length; it can then be further elongated only byapplying tensile forces greater than the original elongating force.

FIGS. 16A-D show pre-compressed spring elements incorporated intopivoting joint assemblies 705, which in turn serve as pins in a chainassembly 707. In each joint assembly, a spring 710 (e.g., a number ofnested Belville springs) is held under compression, and cams 715, whichare rigidly connected to the chain links, cause further compression whenthe flexure force exceeds a threshold. The chain assembly of FIG. 16Ashows the chain with the linear portions b and d bounding a sharply bentportion c, which condition would occur when flexure forces (shown asopposed arrows) exceed the pre-compressed loading of the springelements. In the absence of sufficient flexure forces, the chainassembly remains straight.

FIGS. 16B-D show one of pivoting joint assemblies 705 incorporatingpre-compressed spring 710. The spring is confined by a pair of plates720, each of which has a pair of slots 722 on its circumference. Theplates are driven inward by the rotation of cams 715, to which outerchain links 725 are rigidly attached. Inner chain links 727 are rigidlyattached to a body 730 which holds spring 710 and plates 720. Opposedridges 732 are formed on the inside walls of housing 730 and engageslots 722 to prevent rotation of the plate relative to the housing.

Each cam has a tapered cam face 735 formed with an annular groove 740 toengage a pair of balls 745, which are held in respective depressionsformed in the corresponding plates. The cams are held against the springforce by their mounting 755 on the pin 760, yet are free to rotateindependently. Therefore when sufficient deflecting force is placed onthe chain links, the forces in the pre-compressed spring elements areovercome. The force which is required to rotate a joint through fulltravel depends on the slope of the cam face, and can increase linearlyor non-linearly, depending on the linearity or nonlinearity of theslope.

FIGS. 17A-D show two embodiments of spline assemblies with pressurizedtube elements serving as the constrained spring elements. FIGS. 17A-Bshow an embodiment with the tube elements disposed transversely to thelength of the spline assembly, while FIGS. 17C-D show an embodimentwhere the tubes run along the spline assembly. The tube elements arepressurized with a gas or a compressible liquid such as a siliconefluid; the internal pressurization must be overcome by outsidecompressive forces before the tubes begin to change shape.

FIG. 17A shows components of the transverse-tube element spline assemblywhich are repetitively assembled as spline assembly 765 shown in FIG.17B. The tube elements each have flexible, but non-stretchable externalsleeving 770 which mounds a flexible, fluid-tight inner liner 775. Thetube elements are held in place by spacers 785, each of which hasconcave faces 790 which accept the tube elements and furnish a contactover a significant proportion of the tube. This permits compressionforces to be distributed over a broad area and so meet considerableresistance from internal pressurization. The spacers engage pivot pins800. A set of tensioning cables 795 penetrate spacers 785 and pivot pins800 to form the integrated spline assembly shown in FIG. 17B. The tubeelements over a section e are shown being compressed on the inner sideof the spline assembly curvature; the elements over a section f areshown as they would flatten if bonded to the spacers. In either case theresult is to reduce the internal volume of the tube element, furnishingan increasing internal pressure and so an increasing resistance toflexure.

FIG. 17C shows a spacer 810 for the longitudinal tube embodiment. Thespacer is formed with through-holes 815 and flares 820. The tubeelements are constricted by the through holes and shaped by nesting intothe flares to form a series of pressurized beads 822 as shown in theview of spline assembly 823 in FIG. 17D. The beads are compressed on theinner curvature as shown along section g and extended as shown alongsection h. In both cases the internal volume of the beads is againacting in the same manner as the tube elements in FIGS. 17A-B. The beadswill have a greater resistance to compression if they are isolated onefrom the other, thereby isolating the volume change to each bead. Aclosure element 825 is forced between the through-hole and the tubeelements after the tube is pressurized, thereby eliminating flow betweenbeads. This may be between all beads or only some beads.

FIGS. 18A-D show a spline assembly complete with components forconnecting to a positioner and with bleed tubes for providing a gascushion. While not pertinent to the flexure-controlling properties ofthe assembly, the strip and slide assembly above, and the three bleedtubes below show how flexure-controlling components are integrated intothe full assembly structure.

Spacers 830 are compressed together by tension cables 835 which eitherpossesses elasticity or are coupled to compression springs at the endsof the spline assemblies. The spacers have the opposed faces configuredso that they function as cams. Face portion j, adjacent to thethrough-holes for the tension cables, is flat, while portions k and lare cumbered.

The flexural forces applied to region m of the spline assembly are notsufficient to overcome tension in the cables, so the spacers remainseated against one another on the flat portions and the assembly doesnot curve. The forces applied to region n have exceeded tension in thecables, so that the spacers are free to roll against one another on theportions k. The increasing distance between each spacer at thethrough-hole either progressively stretches the cables or compresses theend springs. Since the line of contact on the spacers movesprogressively further from the through-holes, there is an increasinglygreater resistance to further deflection.

Cross-Section Dimensioner with Pivoting Positioning Elements (FIG. 19)

FIGS. 19A-B show a cross-section dimensioner in which pivoting splinedrive or positioning elements are connected through pin bearingsdirectly to the spline assembly 850. This direct connection ofpositioners to the spline is an alternative to the sliding or rollingcontact shown between positioners and splines in previous figures.

Each positioning element is driven by a computer-controlledvalve/cylinder which functions as a linear actuator 855. Theactuator-positioner combinations 860 are further grouped into robotic"hands," 870 each of which may be independently positioned transverselyand vertically by a two-axis positioner or drive 875. The hands may alsopivot freely or be rotatably driven about a center point 880, as shownin FIG. 19B. If driven, a third rotating positioner would control thepivot angle.

FIGS. 19C-G show in detail a "hand" with pivoting drive elements 890. Acarriage 895, to which each drive element is mounted via a pivot pin900, is carried by ball beatings 910 which run in vertical grooves 915on two opposed slide plates 920. Carriage 815 is vertically positionedby linear actuator 855 as previously described. Pivot pin 900 connectseach drive element 935 to its carriage. The central drive element may befixed rigidly to the carriage so that it does not pivot. It will thenoffer thrust resistance to prevent the spline assembly 850 from shiftinglaterally under asymmetrical forces exerted transversal by the materialbeing formed. This rigid mounting would be employed if a rotatingpositioner were employed to pivot the hand.

A spline pivot pin 940 in turn connects each drive element to a flexibleplate 945 (FIG. 19D) which, along with spline tubes 950 and spline tubebrackets 955, comprises the spline assembly. Each pivot pin connectionof the drive element to the flexible plate constitutes a control pointwhich can be driven into various positions, as shown in FIG. 19A. Thepositions of all of the control points at any one instant determine aparticular configuration or transverse profile into which the splineassembly is flexed.

Incidentally, the gas beating for this type of spline is generated bybleeding gas at a proper temperature through fine perforations in thepressurized spline tubes. The flat surface of the flexible plateconfines gas between itself and the surface of the material beingformed, and so furnishes a bearing without the need for gas to be bledout through the plate surface.

FIG. 19D also shows a simple method of stiffening or adding additionalflexure resistance to the pressurized spline tubes. A wire harness 960supports the tube by being attached from one spline bracket 955 to thenext. Specifically, the harness might be attached to the outer edge ofone tube bracket, be led over the tube to the inside edge of another,and so repeatedly bridge the distance between brackets with tensionedelements. These elements will help to oppose thrusting forces againstthe spline assembly which are caused by resistance to deformation of thesheet material being formed. Other methods might also be employed toincrease the flexure resistance of tube 950, to includeconstrained-spring elements as shown in the earlier FIGS. 16-18.

Stabilizing Element with Internal Spline and Footing Elements (FIG. 20)

FIGS. 20A-D show an arrangement of opposed spline assemblies andchillers. The chillers are continuous elements which are transverselysituated generally parallel to the plane in which the spline assembliesare positioned. They serve as stabilizing elements for the thermoplasticmaterial being formed. Opposed chillers 970 are shown in FIG. 20A in acentered position, as would be assumed if horizontal portions ofmaterial were being stabilized. In FIG. 20B the chillers are shownelevated to an extreme angled position. They are free to travel fromthat position to an equally extreme position below the center of theopposed splines.

The small size of each chiller element, coupled with the inclinedorientations of the slides or positioners 975 upon which they areopposedly carried, permits the elements to be guided through arelatively small linear distance (approximately twice the spline tubediameter) while remaining in opposition to one another through a wideangular range. The result shown is that the thermoplastic sheet beingformed can achieve angles up to eighty degrees from the horizontal.

FIGS. 20C-G show a chiller comprising a flexible coolant containmentchamber 980 which is carried by an small, internal, flexible chillerspline 985 (FIG. 20E), to which the chiller slides 975 are pivotablyattached. The slides may have an air cylinder or other means of applyinga constant slight force to hold the chillers against the sheet materialbeing stabilized. Alternatively, the chillers might be activelypositioned by linear actuators, as previously described in reference tothe cross-section dimensioning spline assembly 850. Such activepositioning would allow the chiller assembly to hold the just-stabilizedpotion of a shape being formed against potential deforming forcesresulting from tension in the formable material.

A coolant 990 flows into the thin-film structure of the containmentchamber. The construction of the chamber is similar to that of an"I-beam" air mattress construction, with flexible ribs connecting theinner and outer faces to one another. A fluid pressure can be maintainedin the chamber to hold its shape, allowing it to be pressed uniformlyagainst the faces of the sheet material. The chamber can also beperforated on the leading edge and on the underside to permit a smallquantity of fluid to bleed out and form a thin lubricating andconducting layer between the chamber and the sheet surface.Additionally, the chiller is designed to conform to any curvature in thesheet, as shown in FIG. 20D.

The thin fill allows conduction of heat from the material beingstabilized to the contained coolant, which is circulated to maintain anear-constant chilled temperate. Entry for the coolant is into thefrontal portion of the chamber, so that the greatest temperaturedifferential, and therefore the fastest cooling rate, is achievedimmediately after initial contact of the chiller or chiller fluid withthe material being formed. In FIG. 20C the sheet material 995 is showntransitions substantially from a stretch-deformable state to astabilized state prior to passing the chiller spline, which imposescontact or support forces against the faces of the sheet.

FIGS. 20E-20G show how the chiller assembly is designed to conform tosurfaces of variable curvature. Flexible footing elements 1000, made ofa very thin sheet of material with elastic spring properties, resideswithin the coolant chamber, and is pre-curved inward (towards thesurface of the materal being stabilized). This curvature allows theelement to maintain continuous contact with a surface of the same or agreater radius of curvature. The footing elements are pin-connected(1010) to chiller spline 985 so that the elements can pivot in the planeof the spline. The pinned fingers 1020 can be convoluted (FIG. 20G) orotherwise configured so that they form a flexible "bridge" between thechiller spline and the leading and trailing edges of the footingelements. FIG. 20F shows a bottom view of the chiller assembly withoutthe containment chamber.

The footing elements can also be formed from fine spring wire bent intoa variety of forms which offer a combination of elasticity and acontrolled range of flexure. They can likewise be formed from any othermaterial or material combination with a configuration which allows thechiller to maintain contact with the range of angled surfaces imposed bythe cross-section dimensioning spline assembly upon the material beingformed.

Conclusion

Thus it can be seen that the invention provides unique new capabilitiesfor generating complex shapes, without the use of dies, molds or otherfixed tooling, in a computer-controlled forming process. The process maybe applied to materials in a stretch-deformable, shear-deformable, orfluent state, or to a combination of materials and components, with theresulting shapes being formed in a single continuous operation. Theinvasion also provides an interactive method for analyzing and modifyinga computer model of a desired shape and for developing a process controldatafile to operate groups of control elements in a forming process.

There are many avenues for further development of continuous moldingprocesses and apparatus. Improvements are being sought in cross-sectiondimensioning rchaisms which reduce their complexities, increase theiraccuracies in assuming curvatures, increase the forces which they canexert on materials, and extend the range of dimensional changes. Animportant improvement in a spline assembly, for instance would be tohave a "detente" force threshold beneath which the assembly wouldmaintain an inflexible linear configuration. Above the "detente"threshold the assembly would begin to flex under positioner loading, yetwould remain so stiff in relation to the resistant forces in thematerial being formed that high accuracy would be maintained for anydegree or complexity of curvature. Another ideal attribute would be forthe spline assembly to curve to very small radii so that relativelysharp comers might be imposed in both axes on formable materials.

Another important improvement would be the capability to "cold form"inelastic sheet materials by imposing high forces while retainingspline-like variability in the dimensioning mechanism. The range ofcandidate materials could be extended to include highly reinforcedthermoplastics, "pre-peg" thermosetting composites which are currentlystamped or matched-die molded, and superplastic metal alloys. Thechallenges are formidable, and may entail the development of entirelynew mechanisms. For instance a "pulling spline" may have to operate inconjunction with the dimensioning mechanism in an intermittent process,with forming principles of the invention being employed in "activeintervals." The shuttle concept described with reference to FIG. 9 mightbe developed into a high strength spline-like form and might flexhorizontally.

Techniques and apparatus might be developed for generating shapes frombias-laid plies of oriented fiber them. Again the challenges areconsiderable if composite constructions of uniform density,predetermined thickness and proper surface smoothness are to begenerated in a single pass through a forming apparatus. A relatedchallenge is to create composite shapes from knitted or woven performs,to incorporate filament winding techniques into the molding process, orto introduce bulk molding compound or other discrete reinforcementmaterials into specific regions as a shape is molded.

Cross-linkable resins might be molded by incorporating a "stabilizing"ultraviolet light source or catalyst-dispensing element into adimensioning mechanism. For instance shell structures might be formed ina bulk liquid resin by either process if the thickness of cross-linkedmaterial were directly dependent on exposure time or distance from the"stabilizer."

A non-obvious candidate for continuous molding might be reinforcedconcrete shell structures. A weight-beating reinforcing mesh would beformed by a moving dimensioning assembly, and a fine-grained concretewould be dispensed under pressure to permeate and coat thereinforcement. A "troweling" or surface-smoothing capability would alsobe incorporated into the trailing edge of the assembly so that afinished shape would be formed and cured in place.

While the above specification describes particular embodiments of theinvention, these should not be construed to be limitations on theinvention's scope, but rather as examples of the invention's broadapplicability. As mentioned above, there are many other usefulembodiments, which might further include apparatus with multiplecross-section determining mechanisms working in concert, systems whichmerge numerous materials (both fluent and deformable) into a singlestructure, and those which combine deformable or thermoplastic materialswith curable materials to include polymers, concrete, ceramic compoundsand the like. While the above is a full description of the preferredembodiments, various modifications, alternative constructions, andequivalents may be used. Therefore, the above description should not betaken as limiting the scope of the invention which is defined by theappended claims.

What is claimed is:
 1. A method of forming a material into apredetermined shape comprising the steps of:establishing relative motionbetween the material and a transition surface through which the materialpasses; imparting cross-sectional dimensions to the material as thematerial passes through the transition surface, the cross-sectionaldimensions conforming to those of the predetermined shape; varying, asthe material passes through the transition surface, at least one of thegroup of variables consisting of the cross-sectional dimensions of thematerial, the rates-of-change of the cross-sectional dimensions of thematerial, the rates of movement of the material relative to thetransition surface, the differential rates of movement of the materialrelative to the transition surface, the instantaneous angles of movementof the material relative to the transition surface, and theinstantaneous differential angles of movement of the material relativeto the tradition surface; abruptly stabilizing the materialsubstantially as it achieves the desired cross-section and angle ofmovement through the transition surface so that the material, as it isstabilized, becomes an addition to a stabilized portion of the formedshape; and controlling the position, orientation, and velocity of theformed shape relative to the transition surface.
 2. The method of claim1 wherein said transition surface is stationary.
 3. The method of claim1 wherein:the material is a thermoplastic material at a temperatureabove its softening temperature when it encounters the transitionsurface; and said stabilizing step comprises chilling at least thesurfaces of the material below the material's softening temperature,preserving the imparted dimensions while the entire material is cooledbelow its softening temperature after it has passed through thetransition surface.
 4. The method of claim 1 wherein:the material is ina fluent state when it encounters the transition surface; and saidstabilizing step comprises chilling at least the surfaces of thematerial below the material's softening temperature, preserving theimparted dimensions while the entire material is cooled so that it is nolonger fluent.
 5. The method of claim 1 wherein:the material is astretch-deformable material; at least one of said imparting and varyingsteps comprises differentially stretching the material; and saidstabilizing step comprises the cessation of shape-determiningstretching.
 6. A method of forming a supply of a material into apredetermined shape comprising the steps of:establishing relative motionbetween the material and a stabilizing element such that the material isin a formable state when it encounters the stabilizing element; engagingthe material along a continuous portion of at least one surface toimpart cross-sectional dimensions to the material as the materialencounters the stabilizing element, the cross-sectional dimensionsconforming to those of the predetermined shape; controlling, as thematerial approaches the stabilizing element, the rates-of-change of thecross-sectional dimensions of the material, the rates of movement of thematerial, the differential rates of movement of the material, theinstantaneous angle of movement of the material, and the instantaneousdifferential angles of movement of the material; using the stabilizingelement to abruptly cause each portion of the material to enter anon-formable state as it achieves the desired cross-section and angle ofmovement past the stabilizing element so that the material, as it isstabilized, becomes an addition to a stabilized portion of the formedshape; and controlling the position, orientation, and velocity of theformed shape relative to the stabilizing element.
 7. The method of claim6 wherein said second-mentioned controlling step comprises exertingtensile forces on the stabilized portion so as to cause the stabilizedportion to exert distributed tensile deforming forces on the materialbeing shaped, thereby deforming every portion of the material, at themoment of stabilization, at a rate and direction of movement determinedby the rate and direction of movement of the just-formed portion of thestabilized portion.
 8. The method of claim 6 wherein said controllingsteps are performed to match the rate and angle of movement of thestabilized portion relative to the stabilizing element to the rate andangle of movement of the material being formed at the moment ofstabilization, thereby preventing the imposition of deforming forces toany portion of unstabilized material.
 9. The method of claim 6 whereinsaid establishing step is performed so that the stabilized portion ofthe shape is stationary and the stabilizing element is moved and angledso as to opposedly match the rate and angle of movement of the materialat the moment of stabilization.
 10. The method of claim 9 wherein thestabilized portion of the shape exerts tensile forces on the materialbeing shaped, thereby deforming the material being shaped.
 11. Apparatusfor forming a material into a predetermined shape comprising:astabilizing element; means for establishing relative motion between thematerial and said stabilizing element such that the material is in aformable state when it encounters the stabilizing element; means forengaging the material along a continuous portion of at least one surfaceto impart cross-sectional dimensions to the material as the materialencounters said stabilizing element, the cross-sectional dimensionsconforming to those of the predetermined shape; means for varying, asthe material approaches said stabilizing element, at least one of thegroup of variables consisting of the cross-sectional dimensions of thematerial, the rates-of-change of the cross-sectional dimensions of thematerial, the rates of movement of the material, the differential ratesof movement of the material, the instantaneous angles of movement of thematerial, and the instantaneous differential angles of movement of thematerial; said stabilizing element causing each portion of the materialto abruptly enter a non-formable state as it achieves the desiredcross-section and angle of movement past said stabilizing element sothat the material, as it is stabilized, becomes an addition to astabilized portion of the formed shape; and means for controlling theposition, orientation, and velocity of the formed shape relative to thestabilizing element.
 12. The apparatus of claim 11 wherein the materialis a thermoplastic sheet, and said means for engaging comprises:a splineassembly having at least one face for engaging a continuous portion ofthe sheet, portions of said spline assembly being relativelypositionable to permit said spline assembly to assume a variety ofdesired configurations; and a positioner array for controlling theconfiguration of said spline assembly.
 13. The apparatus of claim 12wherein said spline assembly engages the sheet from both sides.
 14. Theapparatus of claim 12 wherein said spline assembly engages the sheetfrom one side only.
 15. The apparatus of claim 11 wherein the materialis a thermoplastic sheet that is maintained in a formable state as itencounters said means for engaging, and said stabilizing elementcomprises:cooling elements for causing the sheet to enter a non-formablestate.
 16. Apparatus for forming a thermoplastic sheet into apredetermined shape, comprising:a spline assembly for engaging acontinuous portion of a surface of the sheet, portions of said splineassembly being relatively positionable to permit said spline assembly toassume a variety of desired configurations; a positioner array forcontrolling the configuration of said spline assembly; means for causingthe sheet to be engaged by said spline assembly so that each portion ofthe sheet is in a formable state when each portion is engaged by saidspline assembly; a cooling element for abruptly causing each portion ofthe sheet to enter a non-formable state after each portion has beenengaged by said spline assembly, whereupon each portion of the sheet, asit enters the non-formable state, becomes an addition to a stabilizedportion of the formed shape with cross-sectional dimensions conformingto the predetermined shape; and means for exerting forces on thestabilized portion of the formed shape in a direction away from saidspline assembly as to cause tensile forces to be transmitted to portionsof the sheet that are still in the formable state.
 17. The apparatus ofclaim 16 wherein said means for exerting comprises at least one set ofopposed drive wheels.
 18. The apparatus of claim 16 wherein said meansfor exerting comprises a plurality of transversely separated exitassemblies, capable of exerting differential longitudinal rates ofmovement on said stabilized portion so as to cause differentialstretching of portions of the sheet that are still in the formablestate.
 19. The apparatus of claim 18 wherein at least one of saidplurality of exit assemblies is movable in a direction having acomponent perpendicular to the portion of the sheet engaged by at leastOne of said plurality of exit assemblies.
 20. The apparatus of claim 16wherein said spline assembly includes a fluid manifold to provide afluid cushion for the sheet while the sheet is engaged by said splineassembly.
 21. The apparatus of claim 16 wherein said cooling elementincludes a flexible manifold for distributing a cooling fluid to thesheet.